Improved voltage measurement system using the scanning electron microscope

A method of voltage measurement in the scanning electron microscope (SEM) uses a hemispherical retarding field electron energy analyzer and a feedback control loop. This paper describes improvements made both to the analyzer and the control loop to overcome some of the disadvantages of this system. A compensation technique allows for changes in the incident beam current, and this also reduces the signal caused by specimen topography. Some changes are made to the analyzer geometry which improve the spherical field symmetry of the system, and allow semiconductor devices on circular headers to be examined. The present system is now capable of measuring voltages between 50 mV and 30 V in the presence of beam current fluctuations by a factor of 3 either way. A large loop gain of 100 can now be maintained without difficulty during the voltage measurement line scans across the surface of semiconductor devices, and this ensures lower error in the measurement.